1. Field of the Invention
This invention is directed to test equipment, and more particularly to test equipment for circuit boards.
2. Description of the Related Art
Circuit board testers are used for testing a variety of circuit boards or similar devices to assure that the circuit boards operate as intended. In at least one type of circuit board tester, such as Agilent Model No. 3070, Series 3, a separate device, referred to as a fixture, is used to position the circuit board such that a plurality of electrically conductive probes (which are part of, or coupled to, the tester) contact predetermined components or positions of the circuit board. The particular components or positions that are contacted by the test or probes depend on the tests that are desired. When the probes are in contact with the desired locations on the circuit board, electrical signals with predetermined parameters (e.g., predetermined magnitudes or patterns of current, voltage frequency, phase and the like) are applied by the tester, typically under control of a computer, to certain of the probes. Some or all of the probes are used to measure the performance or response of the circuit board (i.e., to measure electrical parameters at some or all of the probes contacting the circuit board). In this way, it is possible to rapidly perform a number of tests or measurements characterizing the performance of the circuit board while simulating the conditions the circuit board would have, or could have, during actual use. Although it is possible to use these types of tests (and testing devices) for a variety of possible purposes (such as “spot checking” selected circuit boards at a production facility, testing circuit boards which may be malfunctioning, testing prototype circuit boards as part of a design program and the like), in at least some applications, circuit board testing is used to provide quality assurance on all or substantially all products of a given type or class which are produced by a company. Even with the relatively rapid test procedures which can be achieved by in circuit testing, it is not unusual for desired testing of each circuit board to require on the order of 30 seconds to 90 seconds or more.
Because, in at least some applications, circuit board testing is performed on substantially all devices on a production line or production facility, speed and reliability of testing can be especially important since delay or failure at a testing station can delay or interrupt the overall production in a production line or facility. Accordingly, it would be useful to provide a fixture, useable in connection with in-circuit testers, which provides desired speed of positioning the circuit board or other unit under test (UUT) and which achieves a relatively high degree of reliability, e.g., so as to avoid interrupting or delaying production rates at a production line or facility.
The effect of such testing on overall production rates is at least partially related to the rate at which each UUT can be placed in the fixture and the rate at which the fixture can accurately and reliably move the UUT to the desired position or positions. In at least some situations, it is desired to provide a tester with probes at two or more levels (with respect to a direction normal to the plane of the UUT) e.g., by providing some probes having a first height and other probes having a second height. This arrangement affords the opportunity to perform two or more different sets of tests such that the points at which probes contact the UUT during one set of tests are different from (or a subset of) the points at which probes contact the UUT during another set of tests. Typically, in such a “dual stage” testing situation, the UUT is first positioned so as to contact all probes (and perform a first set of tests), and then positioned to contact only the taller set of probes (at points of the UUT which are determined by the location of the tall probes) and a second set of tests are performed using only the taller probes. The order of the tests may be reversed, so that the taller probes contact first, then the shorter probes contact. Although many different testing procedures can be used, as will be understood by those of skill in the art, in at least some situations, the taller probes may be used for functional tests and/or boundary scan tests (such as boundary scan tests as described in IEEE Standard No. 1149.1).
In at least one previous approach, the circuit board is moved in the direction of the probes, typically causing the taller probes, which may be provided with a spring-urged telescoping structure, to partially collapse or telescope, down to the level of the smaller probes, such that substantially both sets of probes (the taller probes and the shorter probes) contact the UUT at desired positions. With the board held in this position, a first set of tests (such as functional tests and/or boundary scan tests) can be performed. After tests are performed using the full set of probes the vacuum is released such that the UUT is positioned to contact only the taller probes (which telescope upwardly) and a second set of tests, (such as tests directed to measuring performance or characteristics of individual components on the UUT) can be performed.
In order for fixtures used in dual stage testing to operate well, especially in the context of a production line or facility, it is also desirable to avoid delays or malfunctions in moving the UUT between the stages. Accordingly, it would be desirable to provide a fixture, useable connection with dual stage in-circuit testing, with a relatively high degree of reliability and operating speed.
In at least one type of fixture, the force of atmospheric pressure is used to move the UUT towards the probes, e.g., by drawing a (partial) vacuum in a sealed area above or near the probes. In these devices, in order to accommodate dual stage testing, such fixtures have, in the past, been provided with a shuttle plate positioned in the area somewhere above the probes and defining one or more standoff structures which engage or contact a surface of the fixture (or of the UUT) to limit the amount of downward movement that the vacuum can effect on the UUT. In this way, the shuttle plate, in a first position, can cause the UUT to be positioned so as to contact only the taller probes. After a first set of tests is performed, the vacuum is at least partially released and the shuttle plate is then moved, typically laterally, such that the standoffs slide against a surface of the fixture sufficiently to become aligned with notches or other openings, allowing the (reapplied) vacuum to pull the UUT down farther, so as to contact the full set of probes (so that a second set of tests can be performed). It is also possible to perform tests with the full set of probes before performing the tests using only the taller probes. In at least one previous device, a shuttle mechanism is located in the lid structure to hold the board down onto the long probes. This device requires pneumatic cylinders, and requires an additional operator connection of compressed air lines to the fixture.
While this arrangement can achieve dual stage positioning, it has been found that such a shuttle plate approach can lead to delays or failures in testing. For example, the shuttle plate approach can provide a relatively high amount of friction when the shuttle plate is moved laterally, particularly when components of the fixture are made of a G10 or similar relatively high-friction material. This can lead to binding (inability of the shuttle plate to move smoothly to the second position or return to the first position). Such binding can not only cause delays and slow down a production line or production facility but can cause failures which may require repairs or replacement of parts, thus creating a substantial interruption of production. Accordingly, it would be useful to provide a fixture that can achieve dual stage testing while avoiding the type of binding, delay, failure, or interruption associated with the use of a shuttle plate.
In at least some systems, pneumatic actuators are used to move the UUT towards the probes. In these types of systems, the pneumatic actuators are configured and/or controlled so as to be movable among three positions, an initial position, a position with the UUT in contact with the taller probes and a position with the UUT in contact with all probes. Pneumatic systems, unfortunately, are associated with certain undesirable qualities. Unlike an atmospheric pressure system, which provides pressure spread over a substantial area, preferably over substantially the entire surface of the UUT, pneumatic systems generally provide pressure only at discrete locations. In general, this leads to a certain amount of flexure of the UUT as it is moved by the pneumatic actuators which can lead to poor contact with the probes in some locations of the UUT and, thus, inaccurate test results. Furthermore, pneumatic systems are generally relatively massive (e.g., such as resulting in fixtures weighing 40 to 50 pounds more than vacuum systems). Generally, this means that changing from one fixture to another (such as for routine maintenance, or to accomplish testing of a different type of UUT) will require two or more workers and/or lifting or positioning equipment, and will typically require more time than changing fixtures in a vacuum system, thus, leading to delays and/or interruptions in a production line or production facility. This is particularly true when the fixture is reinforced in an attempt to reduce the amount of flexure associated with pneumatic systems (although such reinforcement is, typically, only partially successful such that even reinforced systems may have an undesirable amount of flexure). Accordingly, it would be useful to provide a fixture which can be used for dual stage in-circuit testing which has a relatively low weight, e.g., compared with pneumatic-type fixtures, and/or imparts relatively little flexing on the UUT (e.g., compared with pneumatic-type fixtures), and otherwise achieves a low amount or probability of delays or interruptions.
In a prior art system disclosed in U.S. Pat. No. 6,535,008, the UUT, typically supported on a support plate that has perforations corresponding to the probe positions, is held spaced from all of the probes, e.g., by one or more springs. The prior art disclosure uses atmospheric pressure (by drawing a vacuum in the region adjacent the probes) to move the UUT (against one urging of the springs) into a position contacting all of the probes (i.e., both the short probes and the long probes). Such use of atmospheric pressure as a moving force reduces or substantially eliminates flexing of the UUT. In one aspect, in order to move the UUT to a second position, contacting only the tall probes, the vacuum is substantially released but a (preferably actuateable and/or controllable) structure limits the distance the UUT can travel away from the probes (under urging of the springs) so as to position the UUT at the desired location, contacting only the tall probes. Because this movement of the prior art system does not require the lateral sliding of a shuttle plate (or its components), e.g., against a high-friction surface and/or because this movement does not require relative sliding or other contact movement while components are pressed together by atmospheric pressure forces (since the vacuum has already been released, at least partially), there is relatively little tendency for binding during such movement and thus dual stage testing can be achieved with relatively low incidence or probability of delay or failure.
Stated another way, the prior art system of U.S. Pat. No. 6,535,008 uses a retractable arm that, when engaged into a slot, functions as a hard stop to longitudinal motion of the UUT with respect to the probes. At one end of the slot, the UUT is brought into contact with the tall probes, and at the other end, the UUT is brought into contact with the short probes. Any longitudinal motion of the UUT is accomplished by a single stage, driven by a single vacuum feed, and the extent of any longitudinal motion during testing is limited by the engaged retractable arm.
A potential drawback of the prior art system of U.S. Pat. No. 6,535,008 is that it still uses a translatable arm, which increases the complexity of the circuit tester system, and is subject to wear. Accordingly, it would be useful to provide a fixture which can be used for dual stage in-circuit testing which has a relatively low weight, e.g., compared with pneumatic-type fixtures, and/or imparts relatively little flexing on the UUT (e.g., compared with pneumatic-type fixtures), increases reliability by removing any laterally translatable parts, and otherwise achieves a low amount or probability of delays or interruptions.
The testers generally contain a plate as part of the tester that functions as a mechanical stand-off for the fixture. While the fixture is held rigidly in place against the plate, or against rigid stand-offs fastened to the plate, the probes make contact with the circuit board through various holes in the plate. The plates are usually supplied by the tester manufacturer with regularly spaced holes, usually in a rectangular grid, so that a given plate from the tester manufacturer may be used to test a variety of circuits. Even though a circuit generally requires its own custom layout for the probe locations, the plate, because of its standardized hole configuration, may be used relatively independently of the specific locations of the probes, and may also be reused when the tester is reconfigured to test a new circuit. This standardization of the hole locations reduces the number of custom parts required for a tester, and thereby reduces the cost of the system.
The plates are typically molded from a plastic material, such as polycarbonate, so that the array of holes may be built right into the mold. Because they are molded, not drilled, there is no additional cost required for drilling the holes. In addition, the resulting plastic part is non-conducting, which is important for insulation of the electrically conductive probes from each other. These plates are commercially available, and a model that fits the above-mentioned Agilent circuit tester is sold as the “3070 alignment plate”.
A potential drawback to a completely standardized plate is that it generally requires considerable effort to identify particular holes during the final inspection of the tester prior to usage. Typically, a technician will have to verify the location of each probe manually, by counting the row and column values of each probe (seen visually through a hole in the plate), then comparing the values to those in a published list as part of the tester layout drawings. If there are dozens of probes, all specifically located in a rectangular array that contains hundreds of identical-looking holes, this may be a very time-consuming procedure for the technician, and may lead to errors in probe placement if the technician counts incorrectly. Accordingly, it would be useful to provide a plate with simple identification features, so that a technician may readily visually identify which holes are to accept probes.
One prior art solution is to manually mark each hole in the plate that will receive a probe during operation. This solution turns out to be simple in theory, but very labor-intensive, and therefore very expensive. Accordingly, it would be useful to provide a plate with simple identification features that may be identified using the same tools that provide the tester configuration drawings (reducing the possibility of human error in determining the locations.) Additionally, the identification features should be inexpensive, and not require a custom-fabricated plate for each particular circuit under test.